The scaling of metal oxide silicon (MOS) integrated circuits has followed a relentless decrease in feature sizes with a corresponding increase in data throughput per chip for the past thirty years. However, the reduction in power supply voltages in each new generation has not scaled nearly as rapidly as the reduction in feature sizes of the MOS integrated circuits. This mismatch in downward scaling between feature sizes and applied voltages has resulted in substantial increases in electric fields in MOS integrated circuits, particularly in the channels and oxide layers of metal oxide silicon field effect transistors (MOSFETs).
Referring to FIG. 1A, a prior art straight MOSFET is shown having uniform electric fields extending across the gate from the source to the drain. There is an insulating oxide layer between the gate and the channel region in the silicon. As the dimensions of the straight MOSFET decrease, the strength of the electric fields increases, for a given applied voltage. In a conventional MOSFET, current is carried by inversion layer electrons moving under the influence of the lateral electric field in the channel. The channel has two opposing ends that are parallel to each other. The lateral electric field in the MOSFET channel that causes the transistor current to flow varies monotonically from the source, where the field is low, to the drain, where the field peaks sharply. The high field at the drain is well known to cause damage to the MOSFET as carriers are accelerated by the high electric field and some carriers are disadvantageously scattered into the gate oxide leading to damage and poor reliability. This damage limits the current capacity of the MOSFET, and will eventually lead to failure of the MOSFET. The conventional use of lightly doped drains in MOSFET channels has reduced the channel electric fields. However, as the dimensions of the MOSFET features continue to shrink in size, the electric fields will continue to correspondingly increase.
Referring to FIG. 1B, an experimental circular MOSFET has a gate that is curved and extends between the source and drain. The circular MOSFET has a gate structure in the shape of a circle. With a source in the center of the circular gate and a drain on the outside of the circular gate, the electric fields can diverge across the gate from the source to the drain so as to decrease the electric field at the edge of the drain. When the drain is in the center of the circular gate and the source is outside the circular gate, the electric fields into the drain would converge disadvantageously producing an increasing electric field at the edge of the drain. A circular MOSFET has a gate that has no ends, and the circular gate is continuous. A circular MOSFET disadvantageously uses a relatively large amount of silicon square area, relative to the gate size. A conventional serpentine MOSFET, not shown, has a gate with semicircle-curved portions. The serpentine MOSFET structure has one hundred and eighty degree bends that are alternating inflection curve structures. That is, the serpentine MOSFETs have a plurality of one hundred and eighty degree curved bends. The gate is curved one way, and then curved the other way. At each point of curvature change is a curve inflection point. Hence, the serpentine MOSFET has a plurality of curve inflections along the length of the gate. The serpentine MOSFET has a gate and a channel that has two opposing channel ends that are parallel to each other. The channel ends of the gates are defined by two opposing locations under the gate where the underlying channel silicon ends. The semicircle MOSFET has a gate that has two opposing channel ends that are in alignment as well as being parallel to each other. The semicircle MOSFET has a gate and channel in the shape of a horseshoe. The serpentine MOSFET would have both converging and diverging electric fields across the gate at respectively alternating curved-gate portions. As such, the serpentine MOSFET has alternating gate-inflecting portions providing both diverging and converging electric fields. The converging electric field lines disadvantageously provide high electric fields into the drain in the alternating portions of the gate. The semicircle and serpentine MOSFET also disadvantageously require a large relative square area of silicon. These and other disadvantages are solved or reduced using the invention.